To use the banner class built into Give's core use the following

give-addon-banner-activation.php

<?php 
/**
 * Give NAME OF ADD-ON Activation Banner
 *
 * @description: Includes and initializes the activation banner class; only runs in WP admin
 * @hook       admin_init
 */
function give_myaddon_activation_banner() {

	if ( ! class_exists( 'Give_Addon_Activation_Banner' ) && file_exists( GIVE_PLUGIN_DIR . 'includes/admin/class-addon-activation-banner.php' ) ) {
		include GIVE_PLUGIN_DIR . 'includes/admin/class-addon-activation-banner.php';
	} 
	
	if ( ! class_exists( 'Give_Addon_Activation_Banner' ) {
		//bail if class & file not found
		return false;
	}

	//Only runs on admin
	$args = array(
		'file'              => __FILE__,
		//Directory path to the main plugin file
		'name'              => __( 'Myaddon Payment Gateway', 'give-stripe' ),
		//name of the Add-on
		'version'           => GIVE_myaddon_VERSION,
		//The most current version
		'documentation_url' => 'https://givewp.com/documentation/add-ons/myaddon-gateway/',
		'support_url'       => 'https://givewp.com/support/forum/add-ons/myaddon-gateway/',
		'settings_url'      => admin_url( 'edit.php?post_type=give_forms&page=give-settings&tab=gateways' ),
		//Location of Add-on settings page, leave blank to hide
		'testing'           => false,
		//Never leave as "true" in production!!!
	);

	new Give_Addon_Activation_Banner( $args );

	return false;
}

add_action( 'admin_init', 'give_myaddon_activation_banner' );